1. Field of the Invention
The present invention relates to an optical disc reproduction apparatus, and more particularly to an optical disc reproduction apparatus attaining a function to determine whether an optical disc to be reproduced is a read-only optical disc or a recordable optical disc.
2. Description of the Background Art
Types of optical discs include read-only optical discs such as a CD-ROM or a DVD-ROM and recordable optical discs such as a CD-R, a CD-RW, a DVD-R, or a DVD-ROM.
A recordable optical disc has a meandered wobble formed on a circumference in order to maintain its linear velocity constant during reproduction and recording. In the recordable optical disc, as tracking is carried out using the wobble, a signal having a frequency in accordance with a shape of the wobble is superposed on a tracking error signal. The superposed signal is referred to as a wobble signal.
Depending on whether or not the wobble signal is superposed on a tracking signal, whether the optical disc to be reproduced is either a read-only optical disc or a recordable optical disc can be determined. If the optical disc to be reproduced is determined as the recordable optical disc, reproduction of specific contents is disabled. That is, reproduction of the specific contents that have illegally been copied can be avoided.
Japanese Patent Laying-Open No. 2000-182314 discloses a method of determining whether or not a wobble signal is superposed on a tracking error signal. In other words, in Japanese Patent Laying-Open No. 2000-182314, whether or not the wobble signal is superposed is determined with a method noting a zero crossing point as discussed below.
In Japanese Patent Laying-Open No. 2000-182314, a zero crossing point of a tracking error signal is detected so as to calculate a time interval between the zero crossing points. When a difference D between the time intervals is equal to or larger than a prescribed value, a count value is incremented. Then, after a prescribed time has passed, whether the count value is not smaller than the prescribed value is determined. If the count value is not smaller than the prescribed value, it is likely that difference D between the time intervals is equal to or larger than the prescribed value, and therefore, it is determined that the wobble signal is superposed.
On the other hand, with the method of determining whether or not the wobble signal is superposed on the optical disc using the time interval between the zero crossing points as disclosed in Japanese Patent Laying-Open No. 2000-182314, presence/absence of the wobble signal cannot be determined with high accuracy when a large amount of noise component is superposed on the tracking error signal.